In the processing of fabrics, particularly but not limited to knitted fabrics, there may be one or more processing stages in which steam is applied to a moving web of fabric, in order to provide moisture and/or heat thereto. Commonly, steam is applied by means of steam boxes which are positioned on the processing line and extend transversely across the fabric closely above and/or below the surface of the fabric web. A typical steam box is in the form of an enclosed housing extending across the processing line and provided with a narrow, slot-like opening for the discharge of steam against the surface of the fabric.
In a typical fabric processing line, provision is made for adjustments of the various processing mechanisms, in order to accommodate different widths of fabric being processed. A typical steam box, however, is of fixed width, with one or more steam discharge slots extending across its full width. When processing fabric webs of less than the maximum designed width for the processing line, the steam discharge slots are exposed to the fabric web over only a portion of their full width, allowing for the escape of steam in the outer portions of the discharge slots without performing any useful function on the fabric. Some attempts have been made heretofore to minimize such steam losses, as for example by providing a series of hinged flaps along the sides of the steam box (U.S. Pat. No. 4,183,151). However, such previous efforts have not been very satisfactory, and there is a need for a better solution.